In many operating devices for light-emitting means, it is conventional for the light-emitting means to be operated either at a high frequency, in particular in the case of gas discharge lamps, or else by means of pulse modulation, for example in particular in the case of LEDs. For this purpose, so-called driver circuits are provided, which can be in the form of a pulse modulator, a full-bridge or half-bridge circuit, etc. Generally, a DC link voltage is supplied to these driver circuits, which DC link voltage may have a so-called ripple superimposed on it, if appropriate.
In order to provide this DC link voltage, often a so-called PFC (power factor correction) circuit, also referred to as active power factor correction circuit, is used. This PFC circuit generates the DC link voltage on the basis of a generally rectified mains supply voltage whilst maintaining a power factor which is as high as possible.
Within the scope of the present invention, it is always the case of so-called actively clocked PFC circuits, i.e. circuits in which the power consumption by the PFC circuit is preset by a clocking of a switching element, such as, for example, a transistor or a MOSFET. When the switching element is closed, in this case an inductance is magnetized, and this inductance is then discharged when the switch is open via a diode into a storage capacitor. Typical circuits are, for example, a boost converter, an isolated flyback converter or a so-called SEPIC.
The switching element of the PFC circuit and, for example, the switch-on time period Ton of the switching element is generally regulated by a control circuit. It is further known to change the regulator settings depending on externally supplied dimming commands, for example.
A certain problem arises to the extent that, during a transition time after a change in the regulator settings, the energy transmitted by the PFC circuit can be too high or too low. When this transition time of, for example, 40 ms is reached, this temporary excessively high or excessively low transmitted energy is detectable by the human eye in the form of a flash of light or a low light intensity.